SPC AC 121949

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0249 PM CDT WED AUG 12 2015

   VALID 122000Z - 131200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS OVER ERN ND AND NWRN MN...

   ...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE NRN PLAINS/UPPER MS
   VALLEY...

   ...THERE IS A MRGL RISK OF SVR TSTMS OVER THE SERN U.S....

   ...SUMMARY...
   ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS NORTHERN MINNESOTA
   AND FAR EASTERN NORTH DAKOTA WITH SEVERE HAIL AND GUSTY WINDS AS THE
   PRIMARY THREATS. A FEW STRONG TO BRIEFLY SEVERE THUNDERSTORMS ARE
   ALSO POSSIBLE ACROSS A PORTION OF THE SOUTHEASTERN U.S. THIS
   AFTERNOON.

   ...SYNOPSIS...

   MINOR CHANGES HAVE BEEN MADE TO THE 1630Z OUTLOOK.  HAVE LOWERED
   SEVERE PROBS ACROSS THE ARROWHEAD OF MN AND NWRN WI AND FOCUSED MAIN
   CORRIDOR OF HIGHER PROBS ACROSS NWRN MN.  LATEST VIS IMAGERY DEPICTS
   AN EXPANDING/DEEPENING CU FIELD FROM SERN MB...SWD ALONG THE ND/MN
   BORDER.  SOME OF THIS ACTIVITY APPEARS TO BE SLIGHTLY ELEVATED BUT
   BOUNDARY LAYER THERMALS SHOULD DEEPEN CLOSER TO THE WIND SHIFT WHERE
   SFC TEMPERATURES ARE NOW RISING THROUGH THE LOWER 90S.  LATEST
   THINKING IS THUNDERSTORM CLUSTERS COULD DEVELOP SWD FROM ONGOING
   ACTIVITY OVER SERN MB INTO NWRN MN AND GUSTY WINDS/HAIL ARE THE
   PRIMARY THREATS.

   ELSEWHERE...NO CHANGES TO PREVIOUS OUTLOOK WERE MADE.

   ..DARROW.. 08/12/2015

   .PREV DISCUSSION... /ISSUED 1128 AM CDT WED AUG 12 2015/

   ...SYNOPSIS...

   A BLOCKING PATTERN WILL PREVAIL THROUGH THE DAY ONE
   PERIOD...FEATURING RIDGING FROM THE SRN HIGH PLAINS TO NRN ROCKIES
   BRACKETED BY AN UPPER LOW OFF THE WEST COAST AND A LONGER WAVELENGTH
   TROUGH OVER ERN NORTH AMERICA.  WITHIN THIS BROADER-SCALE REGIME...A
   WEAK MID-LEVEL PERTURBATION CURRENTLY CRESTING THE RIDGE OVER ERN
   SASKATCHEWAN INTO CNTRL MANITOBA WILL PROGRESS SEWD INTO THE UPPER
   GREAT LAKES IN ADVANCE OF AN UPSTREAM SYSTEM PIVOTING FROM THE NRN
   ROCKIES INTO NRN PLAINS.

   AT THE SURFACE...A WEAK FRONT/TROUGH ASSOCIATED WITH THE CNTRL
   CANADA IMPULSE WILL PROGRESS SEWD THROUGH PORTIONS OF THE DAKOTAS
   AND MN WHILE ELSEWHERE A WEAK COLD FRONT SETTLES SLOWLY SWD THROUGH
   THE SERN U.S...GULF COAST AND CNTRL TX. 

   ...RED RIVER VALLEY INTO UPPER GREAT LAKES THIS AFTERNOON THROUGH
   EVENING...

   A CLUSTER OF ELEVATED TSTMS IS ONGOING AS OF MID MORNING OVER SRN
   MANITOBA...AIDED BY FORCING FOR ASCENT/DCVA ATTENDANT TO THE
   SHORT-WAVE TROUGH MENTIONED ABOVE.  A SUBSET OF THESE STORMS MAY
   PERSIST INTO AFTERNOON AND BECOME SURFACE-BASED WITH ADDITIONAL
   STORMS FORMING ALONG THE SEWD-MOVING FRONT.  WHILE THE BOUNDARY
   LAYER IS NOT OVERLY MOIST...STRONG DAYTIME HEATING AND STEEPENING
   MID-LEVEL LAPSE RATES FROM THE WEST AND NORTHWEST WILL YIELD
   MODERATE INSTABILITY WITH MLCAPE OF 1500-2500 J/KG.  THIS
   INSTABILITY WILL COINCIDE WITH A VERTICALLY VEERING WIND PROFILE
   WITH STRENGTHENING MID AND UPPER-LEVEL FLOW PROMOTING SUFFICIENT
   VERTICAL SHEAR FOR SUPERCELLS CAPABLE OF LARGE HAIL AND LOCALLY
   DAMAGING WINDS.  THIS SEVERE WEATHER THREAT WILL LIKELY PERSIST
   THROUGH EVENING BEFORE STORMS GRADUALLY WEAKEN OWING TO THE COOLING
   AND RESULTANT STABILIZATION OF THE BOUNDARY LAYER.

   ...SERN U.S. THIS AFTERNOON...

   THE 12Z JACKSONVILLE SOUNDING SAMPLED THE PRESENCE OF A VERY MOIST
   BOUNDARY LAYER WHICH WHEN COUPLED WITH DAYTIME HEATING WILL RESULT
   IN A MODERATE TO STRONGLY UNSTABLE AIR MASS THIS AFTERNOON. 
   LOW-LEVEL CONVERGENCE/UPLIFT ALONG THE COLD FRONT AND DEVELOPING
   SEA-BREEZE FRONT WILL PROMOTE A GRADUAL INCREASE IN STORM COVERAGE
   AND INTENSITY THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE WITH THE
   STRONGEST STORMS CAPABLE OF LOCALLY DAMAGING WINDS.

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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z